Polycarbonate resins have conventionally been known as materials having excellent heat resistance, transparency, mechanical strength, electrical properties, non-toxicity, and other properties. However, they have a drawback of poor flowability.
Various methods have so far been proposed to improve the poor flowability. For example, there is a method of adding a plasticizer to a polycarbonate resin as disclosed in, for example, JP-B-45-39941 and JP-B-48-4100, and a method of using a fatty acid having an aliphatic, long-chain alkyl group, a chloride of such fatty acid, a (long-chain-alkyl)phenol, or the like, which has a plasticizing effect, as a molecular weight modifier or a terminator as disclosed in, for example, JP-B-52-50078. (The term "JP-B" as used herein means an "examined Japanese patent publication".) Of those, the method of using a plasticizer is disadvantageous, although the flowability of the polycarbonate resin is improved, in that plasticizer vapor having a peculiar offensive odor is evolved during molding, and not only does this vapor condense and adhere to mold surfaces and is then transferred to the surfaces of the molded articles produced, thus causing the molded articles to have poor appearances, but also the plasticizer vapor worsens the working atmosphere due to its offensive odor and causes various other problems. The method of introducing a long-chain alkyl group into the terminals of polycarbonate molecules is disadvantageous in that a considerable improvement of flowability cannot be expected because the amount of long-chain alkyl groups which can be introduced into molecular terminals is limited, although this method is free from offensive odors and other problems caused by plasticizers and the flowability is improved to some extent.
Further, polycarbonate resins have conventionally been utilized as an optical material, and known methods for improving the refractive index thereof include a method of introducing a phenyl group, sulfur, a halogen, or the like into the polycarbonate resin structure. However, polycarbonate resins having such a group or element introduced into their structures show poor flowability and, hence, are poor in moldability. In addition, since the refractive indexes of the thus-improved polycarbonate resins are limited to a certain value, it has been difficult to obtain a polycarbonate resin having a low refractive index and a large Abbe number suitable for various purposes of use.